Chemical Reactions and Equations — Important Questions
46 questions
With answersCBSE format
SUMMARY: This chapter introduces students to the basics of chemical reactions and how to represent them using chemical equations. KEY TOPICS: chemical reactions, chemical equations, balancing equations, types of chemical reactions, combination reactions, decomposition reactions, displacement reactions, double displacement reactions, oxidation and reduction, effects of oxidation in everyday life
What is the purpose of balancing a chemical equation?
ATo increase the number of products
BTo ensure the law of conservation of mass is followed
CTo simplify the equation
DTo identify the type of reaction
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Correct answer: Option 2 — To ensure the law of conservation of mass is followed
Q101 Mark
Which of the following is NOT a type of chemical reaction?
ACombination
BDecomposition
CSynthesis
DReduction
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Correct answer: Option 3 — Synthesis
Q111 Mark
In the reaction 2K + 2H₂O → 2KOH + H₂, what is being displaced?
APotassium
BWater
CHydrogen
DOxygen
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Correct answer: Option 3 — Hydrogen
Q121 Mark
Which of the following statements is true about oxidation and reduction?
AOxidation involves loss of protons
BReduction involves gain of electrons
COxidation and reduction can occur independently
DReduction involves loss of oxygen
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Correct answer: Option 2 — Reduction involves gain of electrons
Q131 Mark
What is the product of the reaction between an acid and a base?
ASalt and water
BGas and water
CSalt and gas
DAcid and base
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Correct answer: Option 1 — Salt and water
Q141 Mark
Which of the following is a decomposition reaction?
A2H₂ + O₂ → 2H₂O
B2Na + Cl₂ → 2NaCl
CCaCO₃ → CaO + CO₂
DHCl + NaOH → NaCl + H₂O
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Correct answer: Option 3 — CaCO₃ → CaO + CO₂
Short Answer Questions10 questions
Q153 Marks
What is a chemical reaction? Provide an example.
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A chemical reaction is a process in which substances, known as reactants, undergo a transformation to form new substances called products. For example, when hydrogen gas reacts with oxygen gas, water is formed: 2H₂ + O₂ → 2H₂O.
Q163 Marks
Define a chemical equation and its components.
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A chemical equation is a symbolic representation of a chemical reaction, showing the reactants on the left side and the products on the right side, separated by an arrow. The components include the chemical formulas of the substances involved and their respective coefficients indicating the number of moles.
Q173 Marks
What is the importance of balancing chemical equations?
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Balancing chemical equations is important because it ensures the law of conservation of mass is upheld, meaning that the number of atoms of each element is the same on both sides of the equation. This reflects that matter is neither created nor destroyed in a chemical reaction.
Q183 Marks
Describe a combination reaction with an example.
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A combination reaction is a type of chemical reaction where two or more reactants combine to form a single product. An example is the reaction of magnesium with oxygen to form magnesium oxide: 2Mg + O₂ → 2MgO.
Q193 Marks
What is a decomposition reaction? Give an example.
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A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances. An example is the decomposition of water into hydrogen and oxygen gases: 2H₂O → 2H₂ + O₂.
Q203 Marks
Explain a displacement reaction with an example.
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A displacement reaction occurs when an element in a compound is replaced by another element. For example, in the reaction of zinc with hydrochloric acid, zinc displaces hydrogen: Zn + 2HCl → ZnCl₂ + H₂.
Q213 Marks
What is a double displacement reaction? Provide an example.
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A double displacement reaction involves the exchange of ions between two compounds to form two new compounds. An example is the reaction between sodium sulfate and barium chloride: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl.
Q223 Marks
Define oxidation and reduction in terms of electron transfer.
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Oxidation is the process where an atom or molecule loses electrons, resulting in an increase in oxidation state, while reduction is the gain of electrons, leading to a decrease in oxidation state. These processes always occur simultaneously in a redox reaction.
Q233 Marks
What are the everyday effects of oxidation?
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Oxidation has several everyday effects, such as the rusting of iron when it reacts with oxygen and moisture, leading to structural damage. Another example is the browning of fruits like apples when they are exposed to air, which is due to oxidation.
Q243 Marks
How can you identify a combination reaction from a chemical equation?
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A combination reaction can be identified by observing that two or more reactants combine to form a single product in the chemical equation. The general form is A + B → AB, where A and B are reactants and AB is the product.
Long Answer Questions6 questions
Q256 Marks
Explain the process of balancing a chemical equation. Why is it important to balance chemical equations in chemical reactions? Provide an example of a balanced equation.
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Balancing a chemical equation involves ensuring that the number of atoms of each element is the same on both sides of the equation. This is important because it reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. For example, in the reaction of hydrogen and oxygen to form water, the unbalanced equation is H2 + O2 → H2O. To balance it, we adjust the coefficients to get 2H2 + O2 → 2H2O, which shows that there are four hydrogen atoms and two oxygen atoms on both sides.
Q266 Marks
Describe the different types of chemical reactions and provide an example for each type.
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There are several types of chemical reactions, including combination reactions, decomposition reactions, displacement reactions, and double displacement reactions. In a combination reaction, two or more substances combine to form a single product, such as A + B → AB. A decomposition reaction involves a single compound breaking down into two or more products, like AB → A + B. A displacement reaction occurs when one element displaces another in a compound, such as A + BC → AC + B. Lastly, in a double displacement reaction, the anions and cations of two different compounds exchange places, like AB + CD → AD + CB.
Q276 Marks
What are combination reactions? Describe their characteristics and provide an example.
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Combination reactions are a type of chemical reaction where two or more reactants combine to form a single product. The general form of a combination reaction can be represented as A + B → AB. Characteristics of combination reactions include the formation of a single product and the release or absorption of energy, which can be in the form of heat or light. An example of a combination reaction is the synthesis of water from hydrogen and oxygen: 2H2 + O2 → 2H2O.
Q286 Marks
Explain decomposition reactions and discuss their significance in everyday life. Provide an example of a decomposition reaction.
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Decomposition reactions involve a single compound breaking down into two or more simpler substances. This type of reaction can be represented as AB → A + B. Decomposition reactions are significant in everyday life as they are involved in processes such as digestion, where complex food molecules are broken down into simpler forms. An example of a decomposition reaction is the breakdown of hydrogen peroxide (H2O2) into water and oxygen: 2H2O2 → 2H2O + O2, which is catalyzed by the enzyme catalase in living organisms.
Q296 Marks
What are displacement reactions? Differentiate between single and double displacement reactions with examples.
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Displacement reactions involve the replacement of one element in a compound by another element. In a single displacement reaction, one element displaces another in a compound, represented as A + BC → AC + B. For example, Zn + CuSO4 → ZnSO4 + Cu. In contrast, double displacement reactions involve the exchange of ions between two compounds, represented as AB + CD → AD + CB. An example is Na2S + BaCl2 → BaS + 2NaCl, where the cations and anions switch partners.
Q306 Marks
Discuss oxidation and reduction reactions. How can you identify which substance is oxidized and which is reduced in a reaction?
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Oxidation and reduction reactions, often referred to as redox reactions, involve the transfer of electrons between substances. Oxidation is the process where a substance loses electrons, while reduction is where a substance gains electrons. To identify which substance is oxidized and which is reduced, one can look at the changes in oxidation states. For example, in the reaction 2Mg + O2 → 2MgO, magnesium (Mg) is oxidized from 0 to +2, while oxygen (O2) is reduced from 0 to -2. Thus, Mg is the reducing agent and O2 is the oxidizing agent.
Assertion–Reason Questions8 questions
Q311 Mark
Assertion (A): A chemical reaction involves the transformation of reactants into products.
Reason (R): Chemical equations are used to represent the reactants and products in a chemical reaction.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q321 Mark
Assertion (A): Balancing chemical equations is necessary to obey the law of conservation of mass.
Reason (R): In a balanced equation, the number of atoms of each element is the same on both sides.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q331 Mark
Assertion (A): A combination reaction involves two or more reactants forming a single product.
Reason (R): Decomposition reactions break down a single compound into two or more products.
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Correct answer: Option 3 —
A is true, but R is false.
Q341 Mark
Assertion (A): Oxidation is the loss of electrons or an increase in oxidation state.
Reason (R): Reduction is the gain of electrons or a decrease in oxidation state.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q351 Mark
Assertion (A): In a double displacement reaction, the reactants exchange ions to form new products.
Reason (R): Combination reactions involve the formation of a single product from multiple reactants.
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Correct answer: Option 3 —
A is true, but R is false.
Q361 Mark
Assertion (A): Decomposition reactions can occur through heat, light, or electricity.
Reason (R): All decomposition reactions are endothermic in nature.
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Correct answer: Option 4 —
A is false, but R is true.
Q371 Mark
Assertion (A): A displacement reaction can be classified as either a single or double displacement reaction.
Reason (R): Single displacement reactions involve one element being replaced by another in a compound.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q381 Mark
Assertion (A): Oxidation reactions are always accompanied by reduction reactions.
Reason (R): Oxidation can occur independently without any reduction taking place.
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Correct answer: Option 4 —
A is false, but R is true.
Statement-Based Questions8 questions
Q391 Mark
Statement 1: A chemical reaction involves the transformation of reactants into products.
Statement 2: Chemical equations can only be written for reversible reactions.
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Correct answer: Option 2 —
Only Statement 1 is true.
Q401 Mark
Statement 1: In a combination reaction, two or more substances combine to form a single product.
Statement 2: Decomposition reactions require energy to break down compounds.
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Correct answer: Option 1 —
Both statements are true.
Q411 Mark
Statement 1: Balancing chemical equations ensures that the number of atoms of each element is the same on both sides.
Statement 2: Oxidation is the gain of electrons by an atom or ion.
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Correct answer: Option 3 —
Only Statement 2 is true.
Q421 Mark
Statement 1: A displacement reaction occurs when an element displaces another in a compound.
Statement 2: Double displacement reactions involve the exchange of ions between two compounds.
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Correct answer: Option 1 —
Both statements are true.
Q431 Mark
Statement 1: Oxidation reactions are always exothermic in nature.
Statement 2: Reduction is the process of losing electrons.
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Correct answer: Option 4 —
Both statements are false.
Q441 Mark
Statement 1: In a decomposition reaction, a single compound breaks down into two or more simpler substances.
Statement 2: All chemical reactions are accompanied by energy changes.
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Correct answer: Option 1 —
Both statements are true.
Q451 Mark
Statement 1: The reaction between an acid and a base is an example of a double displacement reaction.
Statement 2: Combination reactions can only involve elements, not compounds.
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Correct answer: Option 1 —
Both statements are true.
Q461 Mark
Statement 1: Oxidation can lead to rusting of iron, which is a significant effect in everyday life.
Statement 2: Chemical equations do not provide information about the physical states of reactants and products.
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Correct answer: Option 2 —
Only Statement 1 is true.
